Induction motor rotor, induction motor, compressor, fan, and air conditioner

ABSTRACT

To provide an indication motor rotor capable of improving motor performance by concentrating portions under magnetic saturation conditions of rotor teeth. The rotor  1  of an induction motor of this invention may include slots  3  formed approximately in the shape of a T. The slots  3  may be formed so that top slots  3   a  are arranged on an outer peripheral portion of a rotor core  1   a , and bottom slots  3   b  are arranged on an inner side of the top slots  3   a . The width in the circumferential direction of the top slot  3   a  is wider than the width in the circumferential direction of the bottom slot  3   b,  and the width in the circumferential direction of a rotor tooth  4  between adjacent top slots  3   a  is narrower than the width in the circumferential direction of the rotor tooth  4  between adjacent bottom slots  3   b.

TECHNICAL FIELD

The present invention relates to an induction motor rotor, and more particularly to the shape of slots of the induction motor rotor. The present invention further relates to an induction motor using the induction motor rotor, a compressor and a fan that are equipped with the induction motor, and an air conditioner that is equipped with the compressor and the fan.

BACKGROUND ART

Various shapes of induction motor rotor have been proposed by the use of double squirrel-cage shapes or the like for the purpose of improving locked-rotor torque, breakdown torque, and efficiency.

As an example, a rotor for a rotating electrical machine having a double squirrel-cage rotor core has been proposed (see e.g., Patent Document 1). The double squirrel-cage rotor core is formed to have intermediate bars fitted in slit portions that connect outside slots and inside slots. The intermediate bars are narrow near the outside slots and wide near the inside slots.

-   -   Patent Document 1: Unexamined Japanese Utility Model Publication         No. SHO 62-68468

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

The rotor described in Patent Document 1 is characterized by its double squirrel-cage shape and the shape of the intermediate bars designed to improve motor performance. However, the rotor is formed to have the slit portions connecting the outside slots on the outer side of the rotor and the inside slots on the inner side of the rotor. The slit portions cause the slots to extend towards the center of the rotor. The problem is that slot spaces cannot be extended in a well balanced design where the width of the rotor teeth (portions of the rotor core between slots) is fixed and thereby a constant density of magnetic flux of the rotor teeth is maintained.

The present invention is directed to solving problems as described above. It is an object of the present invention to provide an indication motor rotor, an induction motor, a compressor, a fan, and an air conditioner, which are capable of enhancing motor performance by concentrating portions of rotor teeth under magnetic flux saturation.

Means to Solve Problems

An induction motor rotor according to this invention may include a rotor core with slots formed therein, and a squirrel-cage secondary conductor having a nonmagnetic and conductive material filled in each of the slots of the rotor core. Each of the slots may be formed so that a width in the circumferential direction of a rotor tooth between adjacent slots is narrower on the outer peripheral side of the rotor core than on the center side of the rotor core.

An induction motor rotor according to this invention may include a rotor core with slots formed therein, and a squirrel-cage secondary conductor having a nonmagnetic and conductive material filled in each of the slots of the rotor core. Each of the slots may be formed approximately in the shape of a T, and include a top slot arranged at an outer peripheral portion of the rotor core and a bottom slot arranged on an inner side of the top slot. Each of the slots may be formed so that a width in the circumferential direction of the top slot is wider than a width in the circumferential direction of the bottom slot. Each of the slots may be formed so that a width in the circumferential direction of a rotor tooth between adjacent top slots is narrower than a width in the circumferential direction of the rotor tooth between adjacent bottom slots.

An induction motor rotor comprising according to this invention may include a rotor core with slots formed therein, and a squirrel-cage secondary conductor having a nonmagnetic and conductive material filled in each of the slots of the rotor core. Each of the slots may be formed approximately in the shape of a T, and include a top slot arranged at an outer peripheral portion of the rotor core and a bottom slot arranged on an inner side of the top slot, Each of the slots may be formed so that a width in the circumferential direction of the top slot is wider than a width in the circumferential direction of the bottom slot. Each of the slots may be formed so that a width in the circumferential direction of a rotor tooth between adjacent top slots is narrower than a width in the circumferential direction of the rotor tooth between adjacent bottom slots. Each of the slots may be formed to include a leakage slot between the top slot and the bottom slot. Each of the slots may be formed so that a width in the circumferential direction of the rotor tooth between adjacent leakage slots is wider than the width in the circumferential direction of the rotor tooth between the adjacent top slots and wider than the width in the circumferential direction of the adjacent bottom slots.

According to the induction motor rotor of this invention, A may be defined as a width in the radial direction of the top slot, B may be defined as a width in the radial direction of the bottom slot, and A<0.5B.

According to the induction motor rotor of this invention, A may be defined as a width in the radial direction of the top slot, C may be defined as the width in the circumferential direction of the top slot, and A<0.5C.

According to the induction motor rotor of this invention, the rotor core may be formed to layer electromagnetic steel sheets. A width in the radial direction of the leakage slot may be substantially equal to the thickness of an electromagnetic steel sheet.

An induction motor rotor according to this invention may include a rotor core with slots formed therein, and a squirrel-cage secondary conductor having a nonmagnetic and conductive material filled in each of the slots of the rotor core. Each of the slots may be formed to include a top slot, a middle slot, and a bottom slot, each of which communicates with an adjacent layer slot. A relation among a width in the circumferential direction of the top slot, a width in the circumferential direction of the middle slot, and a width in the circumferential direction of the bottom slot may be defined as: width in the circumferential direction of the top slot>width in the circumferential direction of the middle slot>width in the circumferential direction of the bottom slot. A relation among a width in the circumferential direction of the rotor tooth between adjacent top slots, a width in the circumferential direction of the rotor tooth between adjacent middle slots, and a width in the circumferential direction of the rotor tooth between adjacent bottom slots may be defined as: width in the circumferential direction of the rotor tooth between adjacent top slots<width in the circumferential direction of the rotor tooth between adjacent middle slots<width in the circumferential direction of the rotor tooth between adjacent bottom slots.

According to the induction motor rotor, G may be defined as a width in the radial direction of the top slot, H may be defined as a width in the radial direction of the middle slot, I may be defined as a width in the radial direction of the bottom slot, and G+H<0.5I.

The induction motor rotor according to this invention may further include a bridge between the top slot and the outer edge of the rotor core. A width in the radial direction of the bridge may be approximately fixed.

An induction motor rotor according to this invention may include a rotor core with slots formed therein, and a squirrel-cage secondary conductor having a nonmagnetic and conductive material filled in each of the slots of the rotor core. Each of the slots may be formed approximately in the shape of a triangle so that a width in the circumferential direction of a rotor tooth between adjacent slots increases towards the center of the rotor core. A width in the radial direction of a bridge between the slot and the outer peripheral edge of the rotor core may be approximately in a fixed workable minimum size.

According to the induction motor rotor, the width in the circumferential direction of the top slot may be wider than a width in the circumferential direction of an opening formed on an inner peripheral portion of a slot of a stator.

According to the induction motor rotor, the slot of the rotor core may include an opening that opens to outside at the outer edge of the rotor core.

An induction motor according to this invention may include the induction motor rotor described above.

A compressor according to this invention may include the induction motor described above.

A fan according to this invention may include the induction motor described above.

An air conditioner according to this invention may include the compressor described above.

EFFECTS

An induction motor rotor of this invention may enhance induction motor performance by concentrating portions under magnetic saturation conditions by forming slots so that a width in the circumferential direction of a rotor tooth between adjacent slots on the outer peripheral side of a rotor core is narrower than a width in the circumferential direction of the rotor tooth between adjacent slots on the center side of the rotor core.

BEST MODE FOR IMPLEMENTING THE INVENTION EMBODIMENT 1

FIG. 1 and FIG. 2 are diagrams illustrating a conventional induction motor 100 for the purpose of comparison. FIG. 1 shows a cross section of a rotor 1 (including a stator 2) of the induction motor 100. FIG. 2 shows a perspective view of the rotor 1 where slots are filled with a nonmagnetic and conductive material (e.g., aluminum, copper, etc.) by die-casting or the like, end rings 7 are fitted at the end portions of the rotor 1.

The cross sectional view of the induction motor 100 of FIG. 1 includes omissions of the winding, etc. of the stator 2.

The stator 2 is formed like a ring with a plurality of slots 2 a and teeth 2 b between slots 2 a formed on the inner peripheral side. The outer peripheral side of the stator 2 is a core back 2 c as a flux path. The rotor 1 is placed inside the stator 2 with an air-gap in between.

The configuration of a rotor core 1 a of the rotor 1 is now described. The rotor core 1 a is formed to include a plurality of slots 3 with rotor teeth 4 arranged between adjacent slots 3 on the outer peripheral side. A shaft hole 6 is provided at a center portion of the rotor core 1 a to allow a drive shaft (not shown in the figures) to fit in. A portion of the rotor core between the slots 3 and the shaft hole 6 is called a core back.

In the rotor 1, aluminum or the like is cast in the slots 3 to form a squirrel-cage secondary conductor or a squirrel-cage winding. The squirrel-cage winding is formed so that a plurality of aluminum bars formed in the slots 3 is mutually short-circuited at each by means of an end ring 7 (see FIG. 2) at the both ends.

With the conventional rotor 1 of FIG. 1, the width in the circumferential direction of the rotor teeth 4 formed between the slots 3 arranged in the circumferential direction of the rotor 1 is fixed. This allows the rotor teeth 4 to maintain a constant density of magnetic flux, as a well balanced design. In this case, the shape of the slots 3 has a width in the circumferential direction gradually reduced from the outside towards the inside.

However, efficiency is increased by reducing secondary resistance (the resistance of the squirrel-cage secondary conductor of the rotor 1). Therefore, if the width in the circumferential direction of the slot 3 is increased so as to extend the space of the slot 3, then the width in the circumferential direction of the rotor tooth 4 is reduced. For this reason, the magnetic saturation of the rotor teeth 4 causes the lowering effect of secondary resistance to be reduced.

Another method for improving the efficiency uses the slots 3 in the shape of a double squirrel-cage. This method has the following characteristics. As a general characteristic of an induction motor using a double squirrel-cage rotor, slip frequency is high when the induction motor is started. Therefore, magnetic flux flows on the outer peripheral side of the rotor, and a secondary current flows exclusively through top slots with high resistance, thereby increasing locked-rotor torque. During a normal operation, slip frequency is low and therefore a secondary current flows through both top slots and bottom slots. This reduces secondary resistance and secondary copper loss, thereby enhancing efficiency.

However, the double squirrel-cage rotor is generally formed to include leakage slots between top slots and bottom slots. Accordingly, slots are extended towards the center of the rotor. Therefore, it is difficult to apply a double squirrel-cage slot in the case where the slots cannot be extended towards the center of the rotor due to wind holes and a drive shaft.

FIG. 3 to FIG. 9 illustrate a first embodiment. FIG. 3 is an enlarged partial top view of the slot 3 in the shape of a T of the rotor core 1 a. FIG. 4 is an enlarged partial top view of the slot 3 in the shape of a double squirrel-cage. FIG. 5 is an enlarged partial top view of the rotor core 1 a illustrating an outer peripheral portion (including the stator 2). FIG. 6 is an enlarged partial top view of the slot 3 in the shape of a double squirrel-cage. FIG. 7 is an enlarged partial top view of the slot 3 in the shape of a T of the rotor core 1 a, as a variant example. FIG. 8 is an enlarged top view of the slot 3 in the shape of a double squirrel-cage, as a variant example. FIG. 9 is an enlarged partial top view of the slot 3 in the shape of a double squirrel-cage for more detail.

FIG. 3 shows the slots 3 formed in the shape of a T. The slot 3 is formed to include a top slot 3 a and a bottom slot 3 b. The top slot 3 a with a wider width in the circumferential direction is arranged in an outer peripheral portion of the rotor core 1 a. The bottom slot 3 b with a narrower width in the circumferential direction is arranged on an inner side of the top slot 3 a (on the center side of the rotor core 1 a). That is, the width in the circumferential direction of the bottom slot 3 b is narrower than the width in the circumferential direction of the top slot 3 a. The top slot 3 a and the bottom slot 3 b are directly connected.

With the slot 3 in the shape of a T, the width in the circumferential direction of the rotor teeth 4 between adjacent slots 3 is narrower at an outer peripheral portion than on the internal side of the rotor 1. More specifically, the width in the circumferential direction of the rotor tooth 4 between adjacent top slots 3 a is narrower than the width in the circumferential direction of the rotor tooth 4 between adjacent bottom slots 3 b. It should be noted that the width in the circumferential direction of the rotor teeth 4 between adjacent top slots 3 a and the width in the circumferential direction of the rotor teeth 4 between adjacent bottom slots 3 b may be defined as a minimum tooth width between adjacent top slots 3 a and a minimum tooth width between adjacent bottom slots 3 b, respectively.

Thus, the slot 3 in the shape of a T of FIG. 3 may be formed to reduce the width in the circumferential direction of one part of the rotor tooth 4 (between adjacent top slots 3 a) and increase the width in the circumferential direction of the other part of the rotor tooth 4 (between adjacent bottom slots 3 b). This may help to concentrate portions under magnetic saturation conditions to one part of the rotor tooth 4 (between adjacent top slots 3 a), and thereby reduce magnetic saturation at other parts of the rotor tooth 4 (between adjacent bottom slots 3 b).

If the entire rotor tooth 4 is under magnetic saturation conditions, then the total magnetic permeability of the rotor tooth 4 is reduced. If the slot 3 is formed in the shape of a T, however, magnetic saturation concentrates to one part of the rotor tooth 4 (between the top slots 3 a). This may help to reduce the length (in the radial direction) of a portion of low magnetic permeability, and consequently improve the efficiency of motor performance.

FIG. 4 shows a possible example where the slots 3 are formed in the shape of a double squirrel-cage that connects the top slots 3 a and the bottom slots 3 b by leakage slots 3 c. The width in the circumferential direction of the rotor teeth 4 between adjacent leakage slots 3 c is wider than the width in the circumferential direction of the rotor teeth 4 between adjacent top slots 3 a and wider than the width in the of the rotor teeth 4 between adjacent bottom slots 3 b. It should be noted that the width in the circumferential direction of the rotor tooth 4 between adjacent leakage slots 3 c may be defined as a maximum tooth width between adjacent leakage slots 3 c.

With reference to FIG. 3 and FIG. 4, the size of each part of the slot 3 may be defined as follows:

-   -   A: a width in the radial direction of the top slot 3 a     -   B: a width in the radial direction of the bottom slot 3 b     -   C: a width in the circumferential direction of the top slot 3 a     -   P: a width in the radial direction of the leakage slot 3 c     -   L: a width in the radial direction of a bridge 8

A relation between A and B may be defined as follows.

A<0.5B  (1)

In this expression, the width in the radial direction of the rotor tooth 4 between adjacent top slots 3 a (the width in the radial direction A of the top slot 3 a) to which magnetic saturation is concentrated is narrower than ½ of the width in the radial direction of the rotor tooth 4 between adjacent bottom slots (the width in the radial direction B of the bottom slot 3 b) where magnetic saturation is reduced. If A is greater than ½ of B, then the length of a portion to which magnetic saturation is concentrated is increased, thereby thus resulting in an adverse effect on efficiency. For this reason, A may be less than ½ of B so as to reduce the length of the portion to which magnetic saturation is concentrated. This may help to reduce the influence of the magnetic saturation of the rotor tooth 4 between top slots 3 a on motor performance. Hence, the efficiency of motor performance may be improved.

A relation between A and C may be defined as follows.

A<0.5C  (2)

In this expression, the width in the circumferential direction C of the top slot 3 a is more than twice the width in the radial direction A of the top slot 3 a. More specifically, the length in the circumferential direction of the bridge 8 at the outer peripheral portion of the rotor core 1 a is more than twice the width in radial direction A of the outré layer slot 3 a. Therefore, if the rotor tooth 4 between the top slots 3 a is under magnetic saturation conditions, the bridge 8 is substantially longer than the rotor tooth between the top slots 3 a, because C is more than twice A. This may prevent magnetic flux from leaking to the bridge 8. Hence, magnetic flux may be used effectively.

The bridge 8 is formed thin so as to reduce the amount of magnetic flux leakage at the outer peripheral portion of the rotor core 1 a. The width in the radial direction L of the bridge 8 may be defined as a workable minimum size (in which an electromagnetic steel sheet is durable in punching process). Generally, the workable minimum size allowing an electromagnetic steel sheet to be processed in punching process is substantially equal to the thickness of the electromagnetic steel sheet. The thickness of an electromagnetic steel sheet is around 0.1 mm to 1.5 mm. If the width in the radial direction L of the bridge 8 is fixed by the workable minimum size, then the amount of magnetic flux leakage may be reduced. Hence, magnetic flux may be used effectively.

FIG. 5 shows a case where the width in the circumferential direction C of the top slot 3 a is wider than a width in the circumferential direction S of a slot opening of the slot 2 a of the stator 2. This may help to reduce the amount of magnetic flux leakage (a portion of magnetic flux generated by the winding of the stator 2 that does not link to the slots 3 of the rotor 1). Hence, magnetic flux may be used effectively.

If a fixed portion of the width in the radial direction L of the bridge 8 is wider than the width in the circumferential direction S of the slot opening, then magnetic flux may be used further effectively.

The use of the leakage slot 3 c arranged between the top slot 3 a and the bottom slot 3 b of FIG. 4 may allow the rotor to perform as a double squirrel-cage rotor. However, if the width in the radial direction P of the leakage slot 3 c is wider than appropriate, then the space of the bottom slot 3 b is reduced when the width in the radial direction of the slot 3 is fixed. Accordingly, the space of the slot 3 is reduced as a whole. This may result in increasing the secondary resistance of the rotor 1. If the secondary resistance is increased, then the efficiency of motor performance is reduced.

Therefore, it is preferable that the width in the radial direction P of the leakage slot 3 c is as narrow as possible. Generally, the workable minimum size of the width in the radial direction P of the leakage slot 3 c is substantially equal to the thickness of an electromagnetic steel sheet (0.1 mm to 1.5 mm) forming the rotor core 1 a. The width in the radial direction P of the leakage slot 3 c may therefore be set to a size substantially equal to the thickness of the electromagnetic steel sheet. This may allow the rotor to perform as a double squirrel-cage rotor without increasing the secondary resistance of the rotor 1.

FIG. 6 shows an effective example where the slots 3 of the rotor core 1 a are modified by adding slot openings. The slot 3 of FIG. 6 is formed to add an opening 3 d to the top slot 3 a extending towards the peripheral edge of the rotor core 1 a.

The additional opening 3 d to the slot 3 helps to reduce the amount of magnetic flux leakage (a portion of magnetic flux generated by the winding of the stator core that does not link to the slots 3 of the rotor 1). Therefore, magnetic flux may be used effectively. Hence, the efficiency of motor performance may be improved.

With reference to FIG. 3, FIG. 4, and FIG. 6, the top slots 3 a are in the shape of a rectangle. FIG. 7 shows a case where the top slots 3 a is formed in the shape of an ellipse. FIG. 8 shows a case where the bottom slots 3 b have rounded corners in addition to the top slots 3 a in the shaped of an ellipse. These configurations may help a die to improve punching performance, thereby enhancing productivity. It may be difficult to fill the slots 3 at corners with a nonmagnetic and conductive material (e.g., aluminum, copper, etc.) if the top slots 3 are rectangular in shape. The top slots 3 a in the shape of an ellipse with rounded corners may help to enhance filling efficiency. This may also help to concentrate portions under magnetic saturation conditions, that is, the length in the radial direction of a portion of the rotor tooth 4 under magnetic saturation conditions is reduced. Hence, the efficiency of motor performance may be improved.

FIG. 9 shows a case where the slot 3 is formed to satisfy θ1>θ2 according to this embodiment, where θ1 denotes an angle formed by the both side surfaces of the top slot 3 a and the center of the rotor core 1 a, and θ2 denotes an angle formed by the sides of adjacent top slots 3 a facing each other and the center of the rotor core 1 a. The bottom slots 3 b are formed within θ1, i.e., the angle formed by the top slot 3 a.

The slots 3 thus formed may allow the induction motor 100 to have well balanced locked-rotor torque, breakdown torque (maximum torque) and operation efficiency.

To increase locked-rotor torque, it is effective to increase secondary resistance by reducing the area of cross section of the top slot 3 a. However, to increase efficiency during normal operation, it is necessary to reduce secondary resistance by both the top slot 3 a and the bottom slot 3 b, and thereby reduce secondary copper loss.

To increase locked-rotor torque, it is preferable to reduce θ1 so as to reduce the area of cross section of the top slot 3 a. However, if the area of cross section of the top slot 3 a is reduced, secondary resistance during normal operation is increased. If the length of the bottom slot 3 b is increased towards the center of the rotor core 1 a, then the area of cross section of the bottom slot 3 b may be increased. However, the width of the slot 3 becomes narrower towards the center of the rotor core 1 a (if the width in the circumferential direction of the rotor tooth 4 is fixed). In order to obtain a desired area of cross section under this situation, the bottom slot 3 b may sometimes get too close to the rotary shaft. If the length of the bottom slot 3 b is increased, then the length of the rotor tooth 4 with high magnetic density in the rotor is increased. This may cause inefficiency.

Furthermore, since the width of the slot 3 is reduced towards the center of the rotor core 1 a, it is difficult to fill the bottom slot 3 b with aluminum by die casting at a center portion of the rotor core 1 a. Consequently, secondary resistance cannot be reduced, resulting in possible inefficiency of motor performance.

As another approach, a desired area of cross section of the slot 3 may be obtained by increasing the width in the circumferential direction of the bottom slot 3 b. However, if the width in the circumferential direction of the bottom slot 3 b is increased, the tooth width (the width in the circumferential direction of the rotor tooth 4) as a passage of magnetic flux during normal operation is reduced. If the tooth width is reduced, then magnetic resistance is increased. This may result in increasing the amount of electric current required for obtaining torque during normal operation. This poses a problem of inefficiency of motor performance.

As described earlier, the following effects may be observed according to this embodiment.

-   -   (1) The slot 3 may be formed in the shape of a T. This may         concentrate magnetic saturation to one place of one part of the         rotor tooth 4 (between adjacent top slots 3 a). Therefore, the         length of a portion of low magnetic permeability is reduced,         thereby resulting in improving the efficiency of motor         performance.     -   (2) The same effect may be observed by forming the slot 3 in the         shape of a double squirrel-cage where the top slot 3 a and the         bottom slot 3 b are connected by the leakage slot 3 c.     -   (3) A relation between the width in the radial direction A of         the top slot 3 a and the width in the radial direction B of the         bottom slot 3 b may be defined by A<0.5B. This may help to         reduce the influence of magnetic saturation of the rotor teeth 4         between adjacent top slots 3 a on motor performance.     -   (4) A relation between the width in the radial direction A of         the top slot 3 a and the width in the circumferential direction         C of the top slot 3 a may be defined by A<0.5C. This may help to         prevent magnetic flux from leaking to the bridge 8 if the rotor         tooth 4 between adjacent top slots 3 a are under magnetic         saturation conditions. Hence, magnetic flux may be used         effectively.     -   (5) The width in the radial direction L of the bridge 8 may be         fixed with the workable minimum size (around 0.1 mm-1.5 mm equal         to the thickness of an electromagnetic steel sheet). This may         help to reduce the amount of magnetic flux leakage. Hence,         magnetic flux may be used effectively.     -   (6) The width in the circumferential direction C of the top slot         3 a may be wider than the width in the circumferential direction         S of the slot opening of the slot 2 a of the stator 2. This may         help to reduce the amount of magnetic flux leakage (a portion of         magnetic flux generated by the winding of the stator 2 that does         not link to the slot 3 of the rotor 1). This may contribute to         an effective use of magnetic flux.     -   (7) Portions having the fixed width in the radial direction L of         the bridge 8 may be wider than the width in the circumferential         direction S of the slot opening. This may contribute to a         further effective use of magnetic flux.     -   (8) The width in the radial direction P of the leakage slot 3 c         may be substantially equal to the thickness of an         electromagnetic steel sheet. This may help to allow the rotor 1         to perform as a double squirrel-cage rotor without increasing         secondary resistance.     -   (9) The slot 3 may be formed to include the opening 3 d. This         may help to reduce the amount of magnetic flux leakage (a         portion of magnetic flux generated by the winding of the stator         2 that does not link to the slot 3 of the rotor 1), and         therefore contribute to an effective use of magnetic flux.         Hence, the efficiency of motor performance may be improved.     -   (10) The slot 3 of FIG. 7 includes the top slot 3 a in the shape         of an ellipse. The slot 3 of FIG. 8 modifies the slot 3 of FIG.         7 by making the bottom slot 3 b rounded at the corners on the         outer peripheral side. This may improve the punching performance         of a die, thereby enhancing productivity. In addition to that,         filling efficiency may also be improved without angular corners         when the slots 3 are filled with a nonmagnetic and conductive         material. This may also help to concentrate portions under         magnetic saturation conditions. Hence, the efficiency of motor         performance may be improved.     -   (11) The rotor core 1 a may be formed to satisfy θ1>θ2 where θ1         denotes the angle formed by the both side surfaces of the top         slot 3 a and the center of the rotor core 1 a, and θ2 denotes         the angle formed by the side surfaces of adjacent top slots 3 a         facing each other and the center of the rotor core 1 a. This may         allow the induction motor 100 to obtain well balanced         locked-rotor torque, breakdown torque (maximum torque) and         operation efficiency.

EMBODIMENT 2

FIG. 10 to FIG. 13 illustrate a second embodiment. FIG. 10 is an enlarged partial top view of the slot 3 of the rotor core 1 a, including a top slot, a middle slot, and a bottom slot. FIG. 11 is an enlarged partial top view of the rotor core 1 a illustrating an outer peripheral portion (including the stator 2). FIG. 12 is an enlarged partial top view of the slot 3 of the rotor core 1 a, including a top slot, a middle slot and a bottom slot, as a variant example. FIG. 13 is an enlarged partial top view of the slot 3 of the rotor core 1 a, including a top slot, a middle slot and a bottom slot, as another variant example.

FIG. 10 shows the slots 3 of the rotor core 1 a that include the top slots 3 a, middle slots 3 e, and the bottom slots 3 b. The slots are joined together. A relation among the width in the circumferential direction of the top slot 3 a, the width in the circumferential direction of the middle slot 3 e, and the width in the circumferential direction of the bottom slot 3 b may be as follows: width in the circumferential direction of the top slot 3 a>width in the circumferential direction of the middle slot 3 e>width in the circumferential direction of the bottom slot 3 b. A relation among the width in the circumferential direction of the rotor tooth 4 between adjacent top slots 3 a, the width in the circumferential direction of the rotor tooth 4 between adjacent middle slots 3 e, and the width in the circumferential direction of the rotor tooth 4 between adjacent bottom slots 3 b may be as follows: width in the circumferential direction of the rotor tooth 4 between adjacent top slots 3 a<width in the circumferential direction of the rotor tooth 4 between adjacent middle slots 3 e<width in the circumferential direction of the rotor tooth 4 between adjacent bottom slots 3 b. It should be noted that the widths in the circumferential direction of the rotor tooth 4 between adjacent top slots 3 a, between adjacent middle slots 3 e, and between adjacent bottom slots 3 b may be defined as minimum tooth widths between the respective layer slots.

Therefore, the rotor tooth 4 is formed to have a narrower width in the circumferential direction on the outer peripheral side than on the inner peripheral side.

As described in the first embodiment, the width in the circumferential direction of a part of the rotor tooth 4 may be reduced, and the width in the circumferential direction of the other part of the rotor tooth 4 may be increased. This may help to concentrate portions under magnetic saturation conditions, and thereby reduce magnetic saturation on the other part of the rotor tooth 4. This may prevent the entire rotor teeth 4 from magnetic saturation. Magnetic saturation may be concentrated only on a part of the rotor tooth 4. Therefore, the length of a portion of low magnetic permeability may be reduced, thereby thus improving the efficiency of motor performance. The rotor teeth 4 may also be formed to have three layers as shown in FIG. 10. This may further distribute magnetic saturation, thereby also improving the efficiency of motor performance.

The size of each portion of the slot of FIG. 10 may be defined as follows:

-   -   G: a width in the radial direction of the top slot 3 a     -   H: a width in the radial direction of the middle slot 3 e     -   I: a width in the radial direction of the bottom slot 3 b     -   D: a width in the circumferential direction of the top slot 3 a     -   L: a distance between the top slot 3 a and the outer peripheral         edge of the rotor core 1 a

A relation among G, H, and I may be defined as follows.

G+H<0.5I  (3)

That is, the sum of the width in the radial direction of the rotor tooth 4 between adjacent top slots 3 a where magnetic saturation is concentrated (the width in the radial direction G of the top slot 3 a) and the width in the radial direction of the rotor tooth 4 between adjacent middle slots 3 e (the width in the radial direction H of the middle slot 3 e) is narrower than ½ the width in the radial direction of the rotor tooth 4 between adjacent bottom slots 3 b where magnetic saturation is concentrated (the width in the radial direction I of the bottom slot 3 b). Consequently, the influence of magnetic saturation on the rotor teeth 4 between adjacent top slots 3 a and between adjacent middle slots 3 e may be reduced on motor performance, as described in the first embodiment.

A relation between G+H and D may be defined as follows.

G+H<0.5D  (4)

That is, the width in the circumferential direction D of the top slot 3 a is more than twice the sum of the width in the radial direction G of the top slot 3 a and the width in the radial direction H of the middle slot 3 e. More specifically, the length in the circumferential direction of the bridge 8 at the outer peripheral portion of the rotor core 1 a is more than twice the sum of the width in the radial direction G of the top slot 3 a and the width in the radial direction H of the middle slot 3 e. This may prevent magnetic flux from leaking to the bridge 8 if the rotor tooth 4 between adjacent top slots 3 a and between adjacent middle slots 3 e is under magnetic saturation conditions, as discussed in the first embodiment. Hence, magnetic flux may be used effectively.

Like the first embodiment, the bridge 8 is formed thin so as to reduce the amount of magnetic flux leakage to the outer peripheral portion of the rotor core 1 a. The width in the radial direction L of the bridge 8 is defined as the workable minimum size (in which an electromagnetic steel sheet is durable in punching process). Generally, the workable minimum size in which an electromagnetic steel sheet is durable in punching process is substantially equal to the thickness of an electromagnetic steel sheet. An electromagnetic steel sheet is around 0.1 mm to 1.5 mm in thickness. If the width in the radial direction L of the bridge 8 is fixed with the workable minimum size, then the amount of magnetic flux leakage may be reduced. This may contribute to an effective use of magnetic flux.

FIG. 11 shows a case where the width in the circumferential direction D of the top slot 3 a is wider than the width in the circumferential direction S of the slot opening of the slot 2 a of the stator 2. This may help to reduce the amount of magnetic flux leakage (a portion of magnetic flux generated by the winding of the stator 2 that does not link to the slot 3 of the rotor 1). Hence, magnetic flux may be used effectively.

A portion having the fixed width in the radial direction L of the bridge 8 may be wider than the width in the circumferential direction S of the slot opening. This may contribute to a further effective use of magnetic flux.

FIG. 12 shows a case where the slots 3 of the rotor core 1 a are modified to become open slots, which is also effective. The slot 3 is formed to include the opening 3 d extending from the top slot 3 a through the outer edge of the rotor core 1 a.

The opening 3 d added to the slot 3 may help to reduce the amount of magnetic flux leakage (a portion of magnetic flux generated by the winding of the stator 2 that does not link to the slot 3 of the rotor 1). This may contribute to an effective use of magnetic flux. Hence, the efficiency of motor performance may be improved.

FIG. 13 shows a case where the top slot 3 a and the middle slot 3 e are formed in the shape of an ellipse while those of FIG. 10 to FIG. 12 are in the shape of a rectangle. The top slot 3 a and the middle slot 3 e of FIG. 13 may improve the punching performance of a die, and thereby enhance productivity. Furthermore, the top slots 3 a and the middle slots 3 e of a rectangular shape may cause a difficulty in filling the slots 3 with a nonmagnetic and conductive material (e.g., aluminum, copper, etc.) at angular corners. The top slot 3 a and the middle slot 3 e in the shape of an ellipse may help to improve filling efficiency without angular corners. Additionally, portions under magnetic saturation conditions may be more concentrated (i.e., the length in the radial direction of a portion of the rotor tooth 4 under magnetic saturation conditions is reduced). This may more improve the efficiency of motor performance.

As described earlier, the following effects may be observed according to this embodiment.

-   -   (1) The slot 3 may be formed to include the top slot 3 a, the         middle slot 3 e and the bottom slot 3 b, each of which is         connected with an adjacent layer slot, and satisfy the following         relation: width in the circumferential direction of the top slot         3 a>width in the circumferential direction of the middle slot 3         e>width in the circumferential direction of the bottom slot 3 b.         The slot 3 may also be formed to satisfy the following relation:         width in the circumferential direction of the rotor tooth 4         between adjacent top slots 3 a<width in the circumferential         direction of the rotor tooth 4 between adjacent middle slots 3         e<width in the circumferential direction of the rotor tooth 4         between adjacent bottom slots 3 b. If the slot 3 is thus formed,         then magnetic saturation may be concentrated to one part of the         rotor tooth 4 (between adjacent top slots 3 a and between         adjacent middle slots 3 e). This may help to reduce the length         of a portion of low magnetic permeability. Hence, the efficiency         of motor performance may be improved.     -   (2) The relation between the width in the radial direction I of         the bottom slot 3 b and the sum of the width in the radial         direction G of the top slot 3 a and the width in the radial         direction H of the middle slot 3 e may be defined as G+H<0.5I.         This may help to reduce the influence of magnetic saturation of         the rotor teeth 4 between adjacent top slots 3 a and between         adjacent middle slots 3 e on motor performance.     -   (3) The relation between the width in the circumferential         direction D of the top slot 3 a and the sum of the width in the         radial direction G of the top slot 3 a and the width in the         radial direction H of the middle slot 3 e may be defined as         G+H<0.5D. This may prevent magnetic flux from leaking to the         bridge 8 if the rotor teeth 4 are under magnetic saturation         conditions between adjacent top slots 3 a and between adjacent         middle slots 3 e. Hence, magnetic flux may be used effectively.     -   (4) The width in the radial direction L of the bridge 8 may be         fixed with the workable minimum size (around 0.1 mm to 1.5 mm         equal to the thickness of an electromagnetic steel sheet). This         may help to reduce the amount of magnetic flux leakage. Hence,         magnetic flux may be used effectively.     -   (5) The width in the circumferential direction D of the top slot         3 a may be wider than the width in the circumferential direction         S of the slot opening of the slot 2 a of the stator 2. This may         help to reduce the amount of magnetic flux leakage (a portion of         magnetic flux generated by the winding of the stator 2 that does         not link to the slot 3 of the rotor 1). Hence, magnetic flux may         be used effectively.     -   (6) The portion having the fixed width in the radial direction L         of the bridge 8 may be wider than the width in the         circumferential direction S of the slot opening. This may         contribute to a further effective use of magnetic flux.     -   (7) The slot 3 may be formed to include the opening 3 d. This         may help to reduce the amount of magnetic flux leakage (a         portion of magnetic flux generated by the winding of the stator         2 that does not link to the slot 3 of the rotor 1). This may         contribute to an effective use of magnetic flux. Hence, the         efficiency of motor performance may be improved.     -   (8) The top slot 3 a and the middle slot 3 e may be formed in         the shape of an ellipse. This may help to improve the punching         performance of a die, and thereby enhance productivity. This may         also help to improve filing efficiency for the slots when filled         with a nonmagnetic and conductive material (e.g., aluminum,         copper, etc.), by eliminating angular corners. This may also         help to further concentrate portions under magnetic saturation         conditions. Hence, the efficiency of motor performance may be         further enhanced.

EMBODIMENT 3

FIG. 14 to FIG. 17 illustrate a third embodiment. FIG. 14 is an enlarged partial top view of the slot 3 of the rotor core 1 a formed approximately in the shape of a triangle so that the width of a rotor tooth 4 between adjacent slots 3 increases towards the center of the rotor core 1 a. FIG. 15 is an enlarged partial top view of the rotor core 1 a illustrating an outer peripheral portion (including the stator 2). FIG. 16 is an enlarged partial top view of the slot 3 of the rotor core 1 a formed approximately in the shape of a triangle so that the width of the rotor tooth 4 between adjacent slots 3 increases towards the center of the rotor core 1 a, as a variant example. FIG. 17 is an enlarged partial top view of the slot 3 of the rotor core 1 a formed approximately in the shape of a triangle so that the width of the rotor tooth 4 between adjacent slots 3 increases towards the center of the rotor core 1 a, as a variant example.

FIG. 14 shows the slots 3 formed approximately in the shape of a triangle so that the width in the circumferential direction of the rotor tooth 4 between adjacent slots 3 increases towards the center of the rotor core 1 a. More specifically, a width in the circumferential direction J1 of the rotor tooth 4 on the peripheral side is narrower than a width in the circumferential direction J2 of the rotor tooth 4 on the center side of the rotor core 1 a.

The slot 3 of FIG. 14 is formed so that width L of the bridge 8 between the slot 3 and the outer peripheral edge of the rotor core 1 a is fixed.

As described in the first embodiment, the width in the circumferential direction of a part of the rotor tooth 4 may be reduced, and the width in the circumferential direction of the other part of the rotor tooth 4 may be increased. This may help to concentrate portions under magnetic saturation conditions, and thereby reduce magnetic saturation on the other part of the rotor tooth 4. This may prevent the entire rotor teeth 4 from magnetic saturation. Magnetic saturation may be concentrated only on a part of the rotor tooth 4. Therefore, the length of a portion of low magnetic permeability may be reduced, and consequently the efficiency of motor performance may be improved. As shown in FIG. 14, the width in the circumferential direction of the rotor tooth 4 may be gradually increased towards the center of the rotor core 1 a. This may allow the magnetic density of the rotor tooth 4 to be reduced towards the center of the rotor core 1 a, thereby distributing magnetic saturation. Hence, the efficiency of motor performance may be further improved.

Additionally, the width in the radial direction L of the bridge 8 between the rotor tooth 4 and the outer peripheral edge of the rotor core 1 a may be fixed. This may help to reduce the amount of magnetic flux leakage from the outer peripheral portion of the rotor core 1 a. This may contribute to a highly efficient operation.

FIG. 15 shows a case where a width in the circumferential direction K of the slot 3 on the outer peripheral side may be wider than the width in the circumferential direction S of the slot opening of the slot 2 a of the stator 2. This may help to reduce the amount of magnetic flux leakage (a portion of magnetic flux generated by the winding of the stator 2 that does not link to the slot 3 of the rotor 1). This may contribute to an effective use of magnetic flux.

A portion having the fixed width in the radial direction L of the bridge 8 may be wider than the width in the circumferential direction S of the slot opening of the stator 2. This may contribute to a further effective use of magnetic flux.

FIG. 16 shows an effective example where the slots 3 of the rotor core 1 a are modified by adding slot openings. The slot 3 of FIG. 16 is formed to add an opening 3 d to the top slot 3 a extending towards the peripheral edge of the rotor core 1 a.

The opening 3 d added to the slot 3 may help to reduce the amount of magnetic flux leakage (a portion of magnetic flux generated by the winding of the stator 2 that does not link to the slot 3 of the rotor 1). This may contribute to an effective use of magnetic flux. Hence, the efficiency of motor performance may be improved.

FIG. 17 shows a case where the slots 3 are formed to have rounded corners at both ends on the outer peripheral side of the rotor core 1 a while the slots 3 of FIG. 14 to FIG. 16 are formed with acute-angled corners. The slots 3 of FIG. 17 may improve the punching performance of a die, thereby enhancing productivity. Furthermore, the top slots 3 a and the middle slots 3 e with acute-angled corners on both sides may cause a difficulty in filling the slots 3 with a nonmagnetic and conductive material (e.g., aluminum, copper, etc.) at angular corners. The slots 3 with rounded corners may help to improve filling efficiency without angular corners.

As described earlier, the following effects may be observed according to this embodiment.

-   -   (1) The slot 3 may be formed approximately in the shape of a         triangle so that the width of the rotor tooth 4 between adjacent         slots 3 increases towards the center of the rotor core 1 a.         Therefore, the width in the circumferential direction of the         rotor teeth 4 is gradually extended towards the center of the         rotor core 1 a. Accordingly, the density of magnetic flux of the         rotor teeth 4 may be reduced towards the center of the rotor         core 1 a, thereby distributing magnetic saturation. Hence, the         efficiency of motor performance may be enhanced.     -   (2) The width in the radial direction L of the bridge 8 between         the rotor tooth 4 and the outer peripheral edge of the rotor         core 1 a may be fixed. This may help to reduce the amount of         magnetic flux leakage from the rotor core 1 a from the         peripheral portion. Hence, operation efficiency may be improved.     -   (3) The width in the circumferential direction K of the slot 3         on the outer peripheral side may be wider than the width in the         circumferential direction S of the slot opening of the slot 2 a         of the stator 2. This may help to reduce the amount of magnetic         flux leakage (a portion of magnetic flux generated by the         winding of the stator 2 that does not link to the slot 3 of the         rotor 1). Hence, magnetic flux may be used effectively.     -   (4) The portion having the fixed width L in the radial direction         of the bridge 8 may be wider than the width in the         circumferential direction S of the slot opening of the stator 2.         This may contribute to a further effective use of magnetic flux.     -   (5) The slot 3 formed to include the opening 3 d may help to         reduce the amount of magnetic flux leakage (a portion of         magnetic flux generated by the winding of the stator 2 that does         not link to the slot 3 of the rotor 1). This may contribute to         an effective use of magnetic flux. Hence, the efficiency of         motor performance may be improved.     -   (6) The slot 3 with acute-angled corners may be modified to have         rounded corners on both sides on the outer peripheral side of         the rotor core 1 a. This may improve the punching performance of         a die, thereby enhancing productivity. This may also help to         improve filing efficiency for the slot 3 when filled with a         nonmagnetic and conductive material (e.g., aluminum, copper,         etc.) without angular corners. Additionally, this may also help         to further concentrate portions under magnetic saturation         conditions. Hence, the efficiency of motor performance may be         further improved.

EMBODIMENT 4

A single phase induction motor driven at a constant rate by a single phase power source has locked-rotor torque smaller than a three phase induction motor. Therefore, there is a high demand for improving locked-rotor torque. Starting current is larger than rated current in the case of an induction motor running at a constant rate. Therefore, the induction motor runs with the rotor teeth 4 under magnetic saturation conditions. The shapes of the slots 3 of the rotors 1 described in the first embodiment to the third embodiment may contribute to concentrating magnetic saturation to the outer peripheral portion of the rotor core 1 a, thereby reducing magnetic saturation at the inner side of the rotor teeth 4 (the center side of the rotor core 1 a), and thereby improving locked-rotor torque. The shapes of the slots 3 of the rotors 1 may therefore be effective on a single phase induction motor.

If an induction motor using any one of the rotors 1 described in the first embodiment to the third embodiment is used in a compressor, fan, etc., then the efficiency of the compressor, fan, etc. may be improved. If the compressor, fan, etc. is then used in an air conditioner, the efficiency of the air conditioner may be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

[FIG. 1] A cross section of a rotor 1 (including a stator 2) of a conventional induction motor 100 for the purpose of comparison.

[FIG. 2] A perspective view of the rotor 1 of the conventional induction motor 100 where slots are filled with a nonmagnetic and conductive material (e.g., aluminum, copper, etc.) by die-casting or the like, and end rings are fitted at the end portions of the rotor 1, for the purpose of comparison.

[FIG. 3] An enlarged peripheral top view of a slot 3 formed in the shape of a T of a rotor core 1 a, according to a first embodiment.

[FIG. 4] An enlarged partial top view of the slot 3 formed in the shape of a double squirrel-cage, according to the first embodiment.

[FIG. 5] An enlarged partial top view of the rotor core 1 a illustrating an outer peripheral portion (including the stator 2), according to the first embodiment.

[FIG. 6] An enlarged partial top view of the slot 3 formed in the shape of a double squirrel-cage, according to the first embodiment.

[FIG. 7] An enlarged partial top view of the slot 3 formed in the shape of a T of the rotor core 1 a, as a variant example, according to the first embodiment.

[FIG. 8] An enlarged partial top view of the slot 3 formed in the shape of a double squirrel-cage, as a variant example, according to the first embodiment.

[FIG. 9] An enlarged partial top view of the slot 3 formed in the shape of a double squirrel-cage for more detail, according to the first embodiment.

[FIG. 10] An enlarged partial top view of the slot 3 of the rotor core 1 a, including a top slot, a middle slot, and a bottom slot, according to a second embodiment.

[FIG. 11] An enlarged partial top view of the rotor core 1 a illustrating an outer peripheral portion (including the stator 2), according to the second embodiment.

[FIG. 12] An enlarged partial top view of the slot 3 of the rotor core 1 a, including a top slot, a middle slot and a bottom slot, as a variant example, according to the second embodiment.

[FIG. 13] An enlarged partial top view of the slot 3 of the rotor core 1 a, including a top slot, a middle slot and a bottom slot, as another variant example, according to the second embodiment.

[FIG. 14] An enlarged partial top view of the slot 3 of the rotor core 1 a formed approximately in the shape of a triangle so that the width of a rotor tooth 4 between adjacent slots 3 increases towards the center of the rotor core 1 a, according to a third embodiment.

[FIG. 15] An enlarged partial top view of the rotor core 1 a illustrating an outer peripheral portion (including the stator 2), according to the third embodiment.

[FIG. 16] An enlarged partial top view of the slot 3 of the rotor core 1 a formed approximately in the shape of a triangle so that the width of the rotor tooth 4 between adjacent slots 3 increases towards the center of the rotor core 1 a, as a variant example, according to the third embodiment.

[FIG. 17] An enlarged partial top view of the slot 3 of the rotor core 1 a formed approximately in the shape of a triangle so that the width of the rotor tooth 4 between adjacent slots 3 increases towards the center of the rotor core 1 a, as a variant example, according to the third embodiment.

EXPLANATION OF REFERENCE NUMERALS

1 rotor

1 a rotor core

2 stator

2 a slot

2 b teeth

2 c core back

3 slot

3 a top slot

3 b bottom slot

3 c leakage slot

3 d opening

3 e middle slot

4 rotor teeth

6 shaft hole

7 end ring

8 bridge

100 induction motor 

1. An induction motor rotor comprising: a rotor core with slots formed therein, and a squirrel-cage secondary conductor including a nonmagnetic and conductive material filled in each of the slots of the rotor core, wherein each of the slots is formed so that a width in the circumferential direction of a rotor tooth between adjacent slots is narrower on the outer peripheral side of the rotor core than on the center side of the rotor core.
 2. An induction motor rotor comprising: a rotor core with slots formed therein, and a squirrel-cage secondary conductor including a nonmagnetic and conductive material filled in each of the slots of the rotor core, wherein each of the slots is formed approximately in the shape of a T, and includes a top slot arranged at an outer peripheral portion of the rotor core and a bottom slot arranged on an inner side of the top slot, wherein each of the slots is formed so that a width in the circumferential direction of the top slot is wider than a width in the circumferential direction of the bottom slot, and wherein each of the slots is formed so that a width in the circumferential direction of a rotor tooth between adjacent top slots is narrower than a width in the circumferential direction of the rotor tooth between adjacent bottom slots.
 3. An induction motor rotor comprising: a rotor core with slots formed therein, and a squirrel-cage secondary conductor including a nonmagnetic and conductive material filled in each of the slots of the rotor core, wherein each of the slots is formed approximately in the shape of a T, and includes a top slot arranged at an outer peripheral portion of the rotor core and a bottom slot arranged on an inner side of the top slot, wherein each of the slots is formed so that a width in the circumferential direction of the top slot is wider than a width in the circumferential direction of the bottom slot, wherein each of the slots is formed so that a width in the circumferential direction of a rotor tooth between adjacent top slots is narrower than a width in the circumferential direction of the rotor tooth between adjacent bottom slots, wherein each of the slots is formed to include a leakage slot between the top slot and the bottom slot, and wherein each of the slots is formed so that a width in the circumferential direction of the rotor tooth between adjacent leakage slots is wider than the width in the circumferential direction of the rotor tooth between the adjacent top slots and wider than the width in the circumferential direction of the adjacent bottom slots.
 4. The induction motor rotor according to claim 2, wherein A is defined as a width in the radial direction of the top slot, B is defined as a width in the radial direction of the bottom slot, and A<0.5B.
 5. The induction motor rotor according to claim 3, wherein A is defined as a width in the radial direction of the top slot, B is defined as a width in the radial direction of the bottom slot, and A<0.5B.
 6. The induction motor rotor according to claim 2, wherein A is defined as a width in the radial direction of the top slot, C is defined as the width in the circumferential direction of the top slot, and A<0.5C.
 7. The induction motor rotor according tot claim 3, wherein A is defined as a width in the radial direction of the top slot, C is defined as the width in the circumferential direction of the top slot, and A<0.5C.
 8. The induction motor rotor according to claim 3, wherein the rotor core is formed to layer electromagnetic steel sheets, and wherein a width in the radial direction of the leakage slot is substantially equal to the thickness of an electromagnetic steel sheet.
 9. An induction motor rotor comprising: a rotor core with slots formed therein, and a squirrel-cage secondary conductor including a nonmagnetic and conductive material filled in each of the slots of the rotor core, wherein each of the slots is formed to include a top slot, a middle slot, and a bottom slot, each of which communicates with an adjacent layer slot; wherein a relation among a width in the circumferential direction of the top slot, a width in the circumferential direction of the middle slot, and a width in the circumferential direction of the bottom slot is defined as: width in the circumferential direction of the top slot>width in the circumferential direction of the middle slot>width in the circumferential direction of the bottom slot, and wherein a relation among a width in the circumferential direction of the rotor tooth between adjacent top slots, a width in the circumferential direction of the rotor tooth between adjacent middle slots, and a width in the circumferential direction of the rotor tooth between adjacent bottom slots is defined as: width in the circumferential direction of the rotor tooth between adjacent top slots<width in the circumferential direction of the rotor tooth between adjacent middle slots<width in the circumferential direction of the rotor tooth between adjacent bottom slots.
 10. The induction motor rotor according to claim 9, wherein G is defined as a width in the radial direction of the top slot, H is defined as a width in the radial direction of the middle slot, I is defined as a width in the radial direction of the bottom slot, and G+H<0.5I.
 11. The induction motor rotor according to claim 2 further comprising: a bridge between the top slot and the outer edge of the rotor core; wherein a width in the radial direction of the bridge is approximately fixed.
 12. The induction motor rotor according to claim 3 further comprising: a bridge between the top slot and the outer edge of the rotor core; wherein a width in the radial direction of the bridge is approximately fixed.
 13. An induction motor rotor comprising: a rotor core with slots formed therein, and a squirrel-cage secondary conductor including a nonmagnetic and conductive material filled in each of the slots of the rotor core, wherein each of the slots is formed approximately in the shape of a triangle so that a width in the circumferential direction of the rotor tooth between adjacent slots increases towards the center of the rotor core, and wherein a width in the radial direction of a bridge between the slot and the outer peripheral edge of the rotor core is approximately in a fixed workable minimum size.
 14. The induction motor rotor according to claim 2, wherein the width in the circumferential direction of the top slot is wider than a width in the circumferential direction of an opening formed on an inner peripheral portion of a slot of a stator.
 15. The induction motor rotor according to claim 3, wherein the width in the circumferential direction of the top slot is wider than a width in the circumferential direction of an opening formed on an inner peripheral portion of a slot of a stator.
 16. The induction motor rotor according to claim 2, wherein the slot of the rotor core includes an opening that opens to outside at the outer edge of the rotor core.
 17. An induction motor comprising the induction motor rotor according to claim
 2. 18. A compressor comprising the induction motor according to claim
 17. 19. A fan comprising the induction motor according to claim
 17. 20. An air conditioner comprising the compressor according to claim
 18. 